A wide variety of techniques are available to surgeons for securing sutures or cables within a hole opening in a bone. Screws, rivets, and other types of interference fitting anchors are commonly used.
One type of bone fastener includes an expandable member having an axial channel and an elongated insertion element insertable therein. When the insertion element is driven into the axial channel in the expandable member, an interference or interlocking fit secures the insertion element to the expander, thereby securing the suture within the bone hole opening. Load forces exerted on the suture act directly on the insertion element so that the security of the suture within the bone hole opening depends on the security of the engagement between the insertion element and the expandable member.
In the foregoing circumstances, what is needed is an expandable sheath in which the cable load (bearing force) acts directly on an expandable sheath that is expanded by an expander member for an interference fit within a hole opening in a bone. Such a device would provide the advantage that cable load (bearing force) acts directly on the expandable sheath so that the fastening strength of the anchor is independent of the axial security of engagement between the expander member and the expandable sheath. Such a bone anchoring device avoids the failure mode of expander separation from the expandable sheath under suture loading.